So my last period was July 21st, I had unprotected intercourse July 24th and my period stoped that day. It is now August 25th, no period, but cramping. I also have my normal back ache and knee ache i get when i get my period. I took a cheap safeway brand hpt that says compare to EPT on it [ im pretty broke ], on saturday [ todays monday ] and it came back negitive. Do you think I'm pregnant or what else could it be?